The Beginning of something WILD

The Brettanomyces Masters Project

This MSc. dissertation is the result of my enthusiasm and interest in Sour/Wild ales and their unique flavors and aromas. Over the past decade, Brettanomyces spp. have seen an increasing use in the craft-brewing sector of the industry with a handful of breweries having produced beers that were primary fermented with pure cultures of Brettanomyces spp. This has occurred out of experimentation as relatively little information exists regarding pure culture fermentative capabilities and the aromatic compounds produced by various strains. In October 2008, I started scouring academic databases on-line and at Heriot-Watt’s University library for all the scientific papers I could obtain regarding Brettanomyces yeasts. During the first semester of my Masters studies in Brewing and Distilling I wrote a preliminary literature review concentrating on all aspects of this yeast genus. I became predominantly interested in the microbiology and biochemistry behind pure culture fermentation, especially with regards to volatile compound production. Throughout my search for literature published in scientific journals I found numerous studies that were conducted over the past century on Brettanomyces spp., with only a limited amount of those studies relating to the brewing industry. The information available on pure culture fermentation with Brettanomyces yeasts was inconsistent and inconclusive, leaving a void in the understanding of the overall function of this yeast genus and its application as a fermentative yeast species. The majority of the recent research has focused on enhancing the knowledge of the wine industry. I intend to provide a greater knowledge of the Brettanomyces strains available in the brewing industry through focusing on strain specific fermentation characteristics and identifying the major compounds produced during pure culture anaerobic fermentation in wort.

I started by asking myself, “how does a brewer use Brettanomyces as a pure culture primary fermentation yeast? Under what fermentation conditions is an optimal beer produced? What are the typical aromatic compounds and in what quantities are they found? What about anaerobic vs. aerobic growth and/or fermentation and the so called Custers effect?” With those questions I introduce my research.

I’m particularly interested in the attenuation levels of each strain and volatile, aromatic compounds produced during the fermentation due to the various conditions. Previous studies have observed the production of a few esters, specifically ethyl acetate, ethyl lactate, ethyl caproate, ethyl caprylate, ethyl caprate, and lowered levels of isoamyl acetate by Brettanomyces spp. along with the production of 4-ethyl phenol, 4-ethyl guiaicol, and tetrahydropyridines. These studies however were conducted with regards to Lambic production, Flemish Sour production, and during secondary fermentation in wine. It is the aim of this study to focus on observing the amounts of compounds produced during pure culture Brettanomyces primary fermentation. Through using pure cultures the various esters produced can be quantified and the source of the fruity aromas which are anecdotally reported from pure culture fermentation can be discovered? Through adding varying amounts of lactic acid to the wort prior to fermentation I can observe the formation of ethyl lactate and continue where other research has left off, while further observing the impact lowered pH has on fermentation.

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